Jackson won the Scottish No10 jersey after Dan Parks struggled to get the backs moving in the opening rounds of the Championship.
Jackson's return is a major boost to Glasgow who are still languishing in the wrong half of the table. And Lineen has revealed he always knew his young fly-half was destined for a bright future.
"To have the Scotland No 10 back is really encouraging. He had a slight bang on his leg but it is fine.
"He is raring to go and is calling the shots this week; straight back into it with the confidence of playing the last two games for Scotland, which has helped him a lot.
"Ruaridh has always had the ability but we always seem to want things to be done in a hurry in Scotland and it takes a while.
"You look at Jonny Sexton, you look at the other young tens and the environment they are in and you can see that it takes time.
"Ruaridh is becoming more composed and making more good decisions.
"At international level you do not have much space to operate so you have to make those decisions very quickly, and what I was really pleased about in the Six Nations was that some of his kicking from hand was outstanding while his passing game was quick, effective and accurate. I was really pleased for him.
"I always knew he had the capacity to play international rugby. I remember his first game down at Bath a few years ago when he played well, but you have got to remember that he played well because he got two intercepts.
"The game was okay but what made him stand out was having the audacity to go for the intercepts in what was an opening game.
"I remember the first time I saw him was playing schoolboy rugby at Murrayfield in the sevens on the back pitches and I liked what I saw.
"He was confident and prepared to have a go but you have got to remember he is young. Give him time and he will just get better and better."
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